This invention relates to the field of sealant compositions and more specifically to sealant compositions comprising alkali swellable latex and a pH increasing material as well as methods for using such compositions to service a wellbore.
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (e.g., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is employed to plug and seal off undesirable flow passages in the cement sheath and/or the casing. While a cement slurry is one type of sealant composition used in primary and secondary cementing operations, other non-cement containing sealant compositions may also be employed.
Latex emulsions, which contain a stable water-insoluble, polymeric colloidal suspension in an aqueous solution, are commonly used in sealant compositions to improve the properties of those compositions. For example, latex emulsions are used in cement compositions to reduce the loss of fluid therefrom and to reduce the gas flow potential of the composition as the compositions are being pumped to the annulus. Latex emulsions are also employed to reduce the brittleness of the sealant compositions; otherwise, the compositions may shatter under the impacts and shocks generated by drilling and other well operations. Such sealant compositions may be used for sealing the junction of multilateral wells. In addition, latex emulsions are used to improve the flexibility of sealant compositions.
Moreover, latex emulsions are also mixed with drilling fluids, particularly the non-aqueous type, near loss-circulation zones such as natural or induced fractures, thereby forming solid masses for sealing those zones to prevent the drilling fluids from being lost during drilling.
Drawbacks to using latex emulsions include a lack of sufficient strength and elasticity. For instance, sealant compositions containing latex emulsions may be unable to withstand fluid pressures imposed upon the emulsion by drilling operations. Therefore, there are needs for a latex emulsion having increased resistance to downhole fluid pressures.